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Alaska faces Exxon Valdez clean-up conundrum

By Jessica Hamzelou

More than 20 years after tens of millions of litres of oil spilled from the tanker Exxon Valdez, significant amounts of the black stuff remain hidden under the surface of Alaska’s beaches. Is the remaining oil harmful, or safely degraded? Should it all be cleared up? The debate is dividing researchers.

Hasn’t all the oil been cleaned up already?

Not all of it. Some remains in layers beneath the beaches of Prince William Sound, which bore the brunt of the spill. A study by Michel Boufadel of Temple University in Philadelphia, Pennsylvania, and Hailong Li of China University of Geosciences (Nature Geosciences, DOI&colon; 10.1038/ngeo749) suggests that oil is persisting because microorganisms are poorly supplied with oxygen in these layers and are unable to degrade the oil.

Are these oily layers causing ecological problems?

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That depends on who you ask. Boufadel says that in some areas the oil is only a few centimetres under the surface, and so could be hazardous to foraging sea otters. But Paul Boehm at California-based engineering and science consultancy firm Exponent says that the oil has been degraded into a harmless state. What’s more, Boehm says, the sea otters feed in quite different habitats from those at which oil is sequestered, so the animals would not be endangered even if the oil had not been degraded.

David Santillo of the Greenpeace Research Laboratories at the University of Exeter, UK, describes the situation as “neither one of heavy contamination nor a clean bill of health”. Whilst contamination might not be severe, any traces of oil could still pose a risk to individual animals, he says.

Not severely polluted but not entirely clean then. So should we clean it up?

No, says Olof Linden, a marine ecologist at the World Maritime University in Malmö, Sweden. Oil has persisted in sediment layers for millions of years provided the circumstances are right, and any clean-up of Prince William Sound could do more harm than good. “From an environmental standpoint the oil is of little concern – as long as it is left where it is,” he says.